The invention concerns a power supply circuit of the kind known from the applicant's U.S. Pat. No. 4,899,271 and use of a magnetic circuit with a number of magnetic components integrated on one or more common magnet cores of such a circuit.
The known circuit i.a. comprises a transformer and two reactive components, e.g. choke coils. The three magnetic components are relatively expensive to produce and in addition a disproportionately large amount of core material is required when the three magnetic components are produced separately.
It has been a long-felt desire to be able to cut down on costs and reduce the amount of core material by integrating the three magnetic components on a common magnet core. However, until now this has been impossible as the voltage curve forms do not match for which reason the flux account does not tally. Further, a transformer's magnetizing current normally causes certain problems, as besides entailing increased loss it may also interact with the load current at low loads and thereby create unfortunate imbalance situations in the power supply circuit.
However, a certain economy has been achieved, as stated in the above patent specification, by integrating the two choke coils on the same core. e.g. by placing each of the choke coils on the outer legs of an E-core. Each of these outer legs must, however, then be provided with an air gap to avoid saturation of the core material, whereas the central leg must be without air gap to avoid coupling between the two choke coil circuits.
Other examples are known where several magnetic components are integrated on a common core, as is the case e.g. with a 3-phase transformer; however, in these cases the curve forms of the flux of the components are uniform but phase displaced so that the flux account tallies.